Yes, that’s creating some kind of circular dependency, node tree using the material which uses the node tree…

Sergey, you may have some advice here?

Maybe skip adding users to node trees who's IDs are the tree owner? Something like http://www.pasteall.org/57712/diff

Not sure how reliable it is, and it needs to be thought carefully, so we don't delete some datablock by accident.

@Campbell Barton (campbellbarton), do you have any strong opinion here?

@Sergey Sharybin (sergey), it can work but in that case other areas need to respect user count too,

Would need a custom set function in def_sh_material (which would conditionally adjust the user count). - also, ntreeSwitchID_ex, BKE_node_tree_unlink_id ... so worth checking on solution, but would want to make sure its working for all areas that access node->id

@Campbell Barton (campbellbarton), BKE_node_tree_unlink_id does not do user counting, but ntreeSwitchID_ex will indeed give problems. Annoying thing is that it's not always known for sure where the node tree is coming from. Suggested approach will end up passing owner of node tree to those functions, which is rather annoying.

Unless there's some better ideas here would rather move this to TODO, maybe even something related to assets works which is being happened now.